The invention relates to a method of inventorying data carriers by means of a communication station, wherein said communication station and each data carrier are brought into communicative connection, and wherein each data carrier brought into communicative connection with the communication station generates a response signal enabling the inventorying of the data carrier after at least one operational condition has been fulfilled and supplies said response signal using a transmission start moment that can be chosen from a plurality of transmission start moments.
The invention further relates to a data carrier which is designed for contactless communication with a communication station and which comprises an integrated circuit, which integrated circuit comprises the following means: response signal generation means for generating a response signal and start moment selection means by which a transmission start moment can be selected from a plurality of transmission start moments.
The invention further relates to an integrated circuit for a data carrier, which data carrier is designed for contactless communication with a communication station, said integrated circuit comprising the following means: response signal generation means for generating a response signal and start moment selection means by which a transmission start moment can be selected from a plurality of transmission start moments.
A method as described in the first paragraph, a data carrier as described in the second paragraph, and an integrated circuit as described in the third paragraph above are known from the document EP 0 957 442 B. This known document discloses a method of inventorying data carriers by means of a communication station, which method is often denoted an anticollision method or anticollision procedure. The communication station, often denoted the reader station, and the known data carrier are brought into communicative connection such that the communication station sends an inquiry information to all data carriers present in a communication field. The sufficient energy supply of the data carriers present in the communication field and the faultless reception of the inquiry information in each data carrier each constitute an operational condition which is to be fulfilled before each respective data carrier generates a response signal which renders possible the inventorying of the relevant data carrier. The inquiry information initializes the start of a sequence of N consecutive time windows both in the reader station and in the data carriers. Each of the N time windows has a given time window duration, which may be fixed or variable. Several sequences of N consecutive time windows are usually generated in a complete anticollision procedure.
Each of the known data carriers comprises a random number generator which randomly lays down one of the N time windows as the return transmission time window, whereby a random transmission start moment is given. The data carrier sends a response information or response signal in the return transmission time window selected by the respective data carrier, which response signal contains the serial number of the data carrier and thus unequivocally characterizes the data carrier. The reader station sends a time window switching information at the end of each time window, such that a switch-over is made from the present time window to the next time window. The reader station identifies the data carriers one after the other and can subsequently, following the completion of the anticollision method, build up and implement a direct communication with one of the data carriers in the communication field each time.
The known solution involves the disadvantage that the entire transaction time for inventorying the known data carriers is comparatively long, because all time windows always have to be worked through.
The invention has for its object to eliminate the above disadvantage and to provide an improved method, an improved data carrier, and an improved integrated circuit.
To achieve the above object, inventive features are provided in a method according to the invention such that a method according to the invention can be characterized as follows:
A method of inventorying data carriers by means of a communication station, wherein said communication station and each data carrier are brought into communicative connection, and wherein each data carrier brought into communicative connection with the communication station generates a response signal enabling the inventorying of the data carrier after at least one operational condition has been fulfilled and supplies said response signal using a transmission start moment that can be chosen from a plurality of transmission start moments, and wherein each data carrier before providing its response signal tests whether another data carrier is already providing its response signal, and wherein each data carrier discontinues the provision of its response signal if another data carrier is already giving its response signal.
To achieve the above object, inventive features are provided in a data carrier according to the invention such that a data carrier according to the invention can be characterized as follows:
A data carrier which is designed for contactless communication with a communication station and which comprises an integrated circuit, which integrated circuit comprises the following means: response signal generation means for generating a response signal and start moment selection means by which a transmission start moment can be selected from a plurality of transmission start moments, and response signal recognition means designed for recognizing a response signal given by another data carrier and for generating and giving off a response signal recognition signal, and wherein delivery decision means are provided which release or block a delivery of the response signal in dependence on the response signal recognition signal and the transmission start moment.
To achieve the above object, inventive features are provided in an integrated circuit according to the invention such that an integrated circuit according to the invention can be characterized as follows:
An integrated circuit for a data carrier, which data carrier is designed for contactless communication with a communication station, said integrated circuit comprising the following means: response signal generation means for generating a response signal and start moment selection means by which a transmission start moment can be selected from a plurality of transmission start moments, and response signal recognition means designed for recognizing a response signal given off by another data carrier and for generating and delivering a response signal recognition signal, and wherein delivery decision means are provided which release or block the delivery of the response signal in dependence on the response signal recognition signal and the transmission start moment.
The provision of the inventive features advantageously and in a simple manner achieves that data carriers can be inventoried significantly faster. This is achieved in particular in that a data carrier, which is brought into communicative connection with the communication station, reacts to other data carriers which are also brought into communicative connection with the communication station, i.e. said data carrier tests whether one of the other data carriers is already giving a response signal, such that the former data carrier will only give its response signal if no other data carrier is already giving a response signal at its transmission start moment.
The inventive features further advantageously achieve that, for example with a small number of data carriers which are brought into communicative connection with a communication station, a response signal can be obtained within a shortest possible period of time with a comparatively high probability, which is desirable and highly advantageous in many applications.
The test as to whether another data carrier is already giving its response signal may take place immediately before the delivery of the response signal for each data carrier in the solutions according to the invention. The test, however, may also take place earlier, for example shortly after the generation of the response signal. It was found to be particularly advantageous when each data carrier already before generating its response signal tests whether another data carrier is giving its response signal, such that each data carrier discontinues the generation of its response signal if another data carrier is already giving its response signal. This is advantageous for achieving the most energy-saving operation of each data carrier.
In the solutions according to the invention, the response signal may be formed by an authentication signal. It was found to be highly advantageous if the identification signal is generated as the response signal, in which case the response signal generation means are formed by identification signal generation means. This is particularly advantageous technically for obtaining as simple as possible a circuit arrangement.
The measures of claim 4 provide the advantage that a transmission start moment can be determined in a comparatively simple manner.
The measures of claim 5 provide the advantage that a waiting time is exactly defined. This is important and advantageous in particular for the case in which no data carriers are present in the communication range of the communication station.
The measures of claim 6 provide the advantage that frequent collisions caused by identical transmission start moments of the data carriers are avoided.
Furthermore, the measure of claim 7 advantageously achieves that an already inventoried data carrier does not take part any more in the inventorying process during inventorying of further data carriers, which is very advantageous for making the inventorying as fast as possible.
Furthermore, the measure of claim 10 and of claim 14 provides the advantage that a recognition of a response signal given off by a data carrier can be achieved by comparatively simple means, i.e. in that a carrier signal delivered along with the response signal is recognized.
Furthermore, the measure of claim 11 and claim 15 provides the advantage that the recognition of a response signal can be achieved by comparatively simple means if the data carrier is also constructed as a communication station.
The above and further aspects of the invention will become apparent from the ensuing description of an embodiment and are clarified with reference to this embodiment.
FIG. 1 shows a data carrier 2. The data carrier 2 is designed for contactless communication with a communication station (not shown). A plurality of data carriers 2 are in communicative connection with the communication station in usual applications, such that the data carriers 2 are within a communication range of the communication station. Before reading of data contained in each of the data carriers 2 or writing of data into each of the data carriers 2 can take place, it is necessary to carry out a so-termed inventorying of the plurality of data carriers 2 by means of the communication station which communicates in a contactless manner with the data carriers 2. During such an inventorying process, identification data ID significant for the respective data carrier 2 are transmitted by the respective data carrier 2 to the communication station and stored in the communication station, i.e. for each data carrier 2, so that the identification data ID of all data carriers 2 in communicative connection with the communication station are known in the communication station, which renders it possible for the communication station to come into contact with a respective data carrier 2 in a purpose-oriented and non-interchangeable manner through the use of the identification data ID characteristic of this data carrier 2, for example for reading useful data from the relevant data carrier 2 or storing useful data in the relevant data carrier 2. It is to be noted that identification data ID are not determined for all data carriers 2 that can be brought into communicative connection with the communication station, but that the identification data ID of a data carrier 2 responding first will suffice.